The Design And Fabrication Of Tunable Vertical-cavity Surface-emitting Lasers With Liquid Crystal

Vertical cavity surface emitting laser (VCSEL) is a semiconductor laser which isoriginated from Iga, the doctor of Tokyo University of Technology in1977. The laserlight direction is perpendicular to the cavity surface of VCSEL. The up reflector,active area and down reflector constitute the VCSEL. The effective cavity length ofVCSEL is shorter than edge-emitting laser. There are many advantages of VCSELbecause of its special structure, like low threshold current, easy to link fiber, singlelongitudinal mode, large modulation bandwidth and long life etc. There are a lot ofapplication of VCSEL, like spectroscopy, optical link, gas detection and opticalcommunication etc.People’s requirement to quality and velocity of optical communication becomesmore and more rigorous. For solving the optical source of Dense WavelengthDivision Multiplexing (DWDM), the wavelength tunable VCSEL is proposed andstudied. More than twenty years later, there are four wavelength tunable methods,electro-thermal, electrostatic, piezoelectricity tuning and tuning with liquid crystal.The former three ways are all based on the Micro-Electro-Mechanical System(MEMS) which is a removable structure and easily influenced by the mechanicalvibration. On the other hand, it is difficult to finish the package for VCSEL with thisstructure. And VCSEL with this structure could not be fabricated as large scalecommercially. However, the liquid crystal which has birefringence solves the questionabove. The liquid crystal is embedded in the intracavity of VCSEL. The wavelengthchanges as refractive index of liquid crystal changes. For the study of wavelengthtunable VCSEL with intracavity liquid crystal, this dissertation shows a lot work asfollowed.1. A new structure of wavelength tunable VCSEL with intracavity liquid crystal isproposed. This structure consists three parts, up reflector, Half-VCSEL and liquidcrystal cell. The liquid crystal cell is used to bloom liquid crystal. It consists ofITO (Indium Tin Oxides) tuning electrode, alignment film, spacer and liquidcrystal. Half-VCSEL consists of GaAs substrate, down reflector and active area.The wavelength tunable range is more than20nm. And the output polarization issingle and stable.2. The thickness of liquid crystal and turning angle of liquid crystal moleculeinfluence the tunable, threshold and polarization characteristics. Based on transfermatrix method, we get the optimal thickness is2025nm. The change of VCSELperformance is showed as the liquid crystal molecule turns from0rad to π/2rad. 3. The850-nm VCSEL with different apertures is fabricated. The polarization switchis measured at different temperatures and analyzed by simulating the influencefrom reflectivity of reflector and quantum well gain.4. The850-nm VCSEL with liquid crystal overlay is presented utilizing thebirefringence of nematic liquid crystal. The threshold current, peak of opticalpower and I-P characteristics at different temperatures were measured andanalyzed. And the current between the first polarization hope and the second oneincreases because of the birefringence of liquid crystal.5. The liquid crystal cell part is made by friction alignment. The Half-VCSEL part isfabricated by lithography and etching. These crafts provide useful guideline forthe fabrication of complete wavelength tunable VCSEL with intracavity liquidcrystal.